The present invention relates generally to internal combustion engines, and more particularly, to a crankcase breather assembly for venting of crankcase gases.
Four cycle engines require a crankcase breather to rid the crankcase of pressures caused by blow-by gases escaping past worn piston rings and cylinder walls from the combustion chamber, by the downward force of the piston, and by expansion of the air in the crankcase from increasing heat. The buildup of pressure can eventually cause the oil seals to leak. In order to alleviate pressure buildup, a breather is installed in the crankcase.
Conventional breather valves include a reed valve in which a flexible metal strip is positioned over an opening in the crankcase. The reed opens on the downward piston stroke when the pressure differential between the atmosphere and the crankcase is sufficient to overcome the spring tension of the reed. A second type of breather valve is a disc-type valve that is generally made of a lightweight metal or plastic and moves perpendicular to an opening in the crankcase. The disc is spring biased or gravity biased to a closed position and opens to cover the opening in response to pressure changes.
A third type of breather valve is a molded flexible valve, commonly called a "mushroom" or "umbrella" valve. This valve has a center stem for attachment to a valve seat and covers a circular pattern of holes in the closed position. When crankcase pressure builds, the valve will flex upwardly to uncover the openings and vent the gases.
In U.S. Pat. No. 5,067,449, a crankcase breather assembly is disclosed wherein a plastic valve seat is press fit into a breather passage or opening in the crankcase. A flexible breather valve is secured to the valve seat for venting crankcase gases. In this disclosure, the breather chamber is formed by an upstanding wall that extends upwardly from the top wall of the crankcase. The breather chamber is closed at the top by a removable cover plate and a corresponding sealing gasket.
In some engines the breather chamber, valve seat, and valve are all incorporated into a molded plastic cup that is located in an opening in the crankcase. In particular, the flexible valve is attached to the bottom of the cup having the necessary valve openings therein. The cup is positioned within an opening in the crankcase, and a gasket is positioned over the molded flange at the top of the cup. A metal cover is then positioned over the gasket, and the entire assembly is held in place by several screws, which extend through the cover and crankcase. Some assemblies include a separate breather tube that is connected to the air cleaner assembly.
This breather assembly has performed effectively to maintain a partial vacuum in the crankcase as well as prevent oil from being forced out of the engine oil seals or past the piston rings or any gasket areas. Notwithstanding this successful performance, efforts are continuously directed toward more efficiently producing crankcase breather assemblies.